1. Field of the Invention
The present invention relates generally to the field of telecommunications devices. More specifically, the present invention is directed to systems and methods for improving timing phase estimation in telecommunications equipment.
2. Description of the Related Art
Currently, in the field of analog modem devices, and particularly with respect to the V.92 quick connect phase I, a digital modem transmits QTS signals at the rate of 8000 symbols per second to the analog modem. The QTS signals consist of 128 repetitions of the sequence {+V, +0, +V,−V,−0,−V} where V is defined to be the PCM code word whose Ucode is UQTS and 0 is the PCM code word with Ucode 0[1]. After analog-to-digital conversion of the voice band modem signal and demodulation, the receiver can get a 4 kHz tone. The challenge in this arrangement is to utilize the 4 kHz tone and the converged DFE coefficients to lock the timing phase to the optimal point relative to the symbol interval. The desired result is to adjust the timing interpolator to sample the equalized signal at the maximum eye opening instant. It is recognized that this can be achieved at the phase of (2i+1) π/2, where i ε{integer} of the 4 kHz tone.
Those skilled in the art have recognized that the timing phase should include the phase shifts caused by both the precursor equalizer (linear portion) and post cursor equalizer (decision feedback portion). Is difficult to estimate the phase shift caused by the postcursor EQ because of the fact that the post cursor EQ is usually implemented with a filter and the phase response of the filter is typically non-linear. Furthermore unless the sampling phase is precisely locked at the right point relative to the symbol interval, the decision made by the DFE will be inaccurate. One prior approach to this problem is to utilize the DFE output to perform the estimation. However, there is no correct decision available at that time and the estimation is therefore not accurate enough.
Accordingly, there remains a need in the field for improved estimation of the desired phase. The inventors of the instant application have achieved such a solution which improves performance by achieving the desired phase estimation in less time and through utilizing a less complex system and calculation.